Changes in biliary lipid output after interruption of pravastatin treatment in humans

The use of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (e.g. pravastatin) has gradually increased in the treatment of hypercholesterolaemia. By inhibiting HMG-CoA reductase (the rate-limiting enzyme in cholesterol synthesis) activity, cholesterol synthesis in the liver is reduced and the plasma level of cholesterol, especially low-density lipoprotein (LDL)-cholesterol, is substantially lowered. Simultaneously, inhibition of HMG CoA reductase activity is associated with increased synthesis and accumulation of larger amounts of HMG CoA reductase enzyme protein. The main purpose of this study was to determine if the cessation of pravastatin treatment causes a rapid increase in the synthesis and biliary secretion of cholesterol, a condition which might lead to a temporarily increased cholesterol saturation of bile. Nine patients undergoing surgery for stones in the common bile duct were fitted with T-tubes in the common bile duct peroperatively; the side arm of the T-tube was left open postoperatively, creating a biliary fistula. All patients were given 6 days' treatment with pravastatin (20 mg b.i.d.) following the operation. Bile was collected from the T-tube, in 12-h fractions during this period and for another 3 days after termination of the treatment. Plasma levels of lipoproteins and lathosterol--reflecting cholesterol synthesis--were determined on several occasions. After cessation of pravastatin treatment, the plasma levels of total cholesterol and LDL-cholesterol increased by 21% and 33% respectively. High-density lipoprotein (HDL)-cholesterol did not change. The plasma level of lathosterol was increased two- to fourfold. Outputs of bile acids and phospholipids were significantly increased (23% and 10% respectively) after termination of treatment, whereas the output of cholesterol was not significantly changed. Cholesterol saturation was reduced by 20%, from 175 +/- 37% to 140 +/- 19%, but this change was not significant. The results indicate that, with the present experimental model (biliary diversion), the synthesis and biliary secretion of bile acids seem to be largely dependent on the de novo synthesis of cholesterol in the liver, whereas the biliary output of cholesterol is not.